Process for obtaining dispersions of polyfluorethylenes



Patented Dec. 8, 1953 PROCESS FOR. OBTAINING DISPERSIONS i F POLYFLUOROETHYLENES' Kenneth L. lierry, Hockessin, Del, assignor to I, du Pont de Nemours and Company Wilr niington, Del. a corporation of Delaware.

ti htenin App av- 10, 195-1, genial; No. 225,617

1.1 (fllaims (Cl. 260-295),

c telyst h a ucc n acid. per x e- A.

serious disadvantage of, this procedure is that the, colloid is unstabiliaed and is coagulatedf at very low polymer concentrations by the agitation nec: essary to dissolve the gaseous fluoroethylene monomer. The result is thatthe desired colloidal polymer is obtained in a state. of high dilution h the a ueou t e c i m umine e s t tine the handling of large amounts of water 01, a

given amount of'polymer.

This invention has asan object anew and im proved method for obtaining stable aqueous dispersions of colloidal polymeric completely haloenated' p v w oe vl s w ich d spers ns. contain the polymer in relatively highconcentrationl Other objectswill-appear hereinaf.ter.

I- have found that asurprising increasein concentration ofcolloidal polymeric polyfiuoroeth- -r ylene in aqueous dispersion can be obtained; before coagulation takes place wh en a monomeric completely halogenated polyfluoroethylene in which the halogen presentconsists entirely or fluorine or of fluorine and chlorine, is polymerized inan aqueous mediumcontaininga peroxy polymerization catalyst and a saturated fluorine-containing compound: which isliquidunderv polymerizing conditions for the polyfl-uoroethylene andwhich contains 2-21 carbon atoms,-

not .more than oneihydrogen, not morethan two; chlorines and the remainder of the substituents fluorine; the hydrogen and:chlorine.present being attached to. as linear or annular chaincarbon further substituted only.;with fluorine; The-effect is particularly markedwhen the saturated'fiuorocarbon, compound. contains vonly carbon, fluorine, and chlorine.

The polymerization of: the monomeric polyfiuoroethylenev in the aboveedescribedaqueousmixtureicontaining thefluorine-con-taining;com-

pound ,is. carried out in accordance with; known procedure, which is described in U: S. Patent 2,393 967 and which involves; pressures of from- 1 to D0 atmospheres, andtemperatures offrom- 0 7 C; to 1002 v C in the" presenceof a. peroX-y catathe peroxycatalyst: a modifier such as sodium bisulfite. In addition a small amount. of. water soluble ferrous salt, e. g., ferrous sulfate, is usually present in amount sufficient to provide; from about 0.2 to about parts per million of ferrous ions based on the weight of reaction medium.

In the preferred procedure for carrying out the; present invention, a reaction medium comprising distilled water towhich has been added small amounts of sodium persulfate or other peroxy catalyst, sodium bisulfi-te a trace of a ferrous iron salt, and about 2% ofthe saturated fiuorine= containing compound, based on the total weight of the reaction medium, is charged into a pressure vessel and the vessel is evacuated; Tetrafluoroethylene monomer is introduced until" a suitable pressure, e. g,, about lbp/sq. in. is attained; The closed pressure vessel is heated" to. about 60 C. with agitation until the colloidal polymer formed begins to coagulate. There results a colloidal dispersion of high molecular weight, film-forming polymeric tetrafluoroethylene.

The fluorine-containing coznpounds used in the process of this invention are easily recoveredthe particular method employed depending on the particular fluorine-containing compound being used: In the case of normally gaseous compounds (which are liquid only under the conditions of polymerization), the fluorine-containing com-.

pound is allowed to vaporize out of the colloidal dispersion; Normally liquidfluorine-containing compounds are in: the colloidal dispersion as a separate phase-and are recovered by deoantation: or by steam distillation.

The-following examples, in whichparts are-by weight; illustratethe invention: more specifically;

Escamplel.

Two hundred'andfifty parts ofdistilledwater, 0.125 part of ammonium persulfate, 0:05 part'of sodium bisulfite, 0.001 part ofvFeSOrflHzO; and. 5 parts of perfiuorodimethylcyclohexane (CaFisl are mixed in a pressure vessel (having a' volume capacity of 325 partsof water at room temperature) and the mixture is heated to 60 C. The vesselis evacuated to remove airand thenpressured tobfl-lbz/sq. in: with tetrafluoroethylene; The vessel is: maintained at 60- C. and agitated until the colloidal polymer which forms first begins to coagulate. After 5 hours and 26 minutes; agitation is-stopped and most of the fluorocarbon settles tothebottomof thereaction vessel and can be separated fromthe dispersionof,

ysti. tz ausually a v ous-to'includwitlr 55.; the polytetrafiuoroethylena In this reaction;

3 there is formed a 9.0% by weight aqueous colloidal dispersion of high molecular weight, filmforming polytetrafiuoroethylene.

In a control experiment at 65 C. in which the perfluorodimethylcyclohexane is omitted, coagulation begins after 37 minutes and there is obtained a dispersion containing only 1.16% of polytetrafiuoroethylene.

Example II Two hundred and fifty parts of distilled water, 0.05 part of ammonium persulfate, 0.02 part of sodium bisulfite, 0.001 part of FeSOmI-IzO, and 5 parts of 1,2dichlorohexafiuorocyclobutane (C4C12F6) are mixed in a pressure vessel similar to that of Example I and heated to 50 C. The vessel is evacuated to remove air, pressured to 57 lb./sq. in. with tetrafiuoroethylene, and shaken for 2.5 hours until the colloidal polymer first begins to coagulate. Agitation is stopped and the fluorine-containing compound is allowed to settle out. There is formed a 4.64% solids dispersion of high molecular Weight, tough, film-forming polytetrafiuoroethylene.

A control experiment run without any 1,2-dichlorohexafiuorocyclobutane afforded only a 0.65% solids dispersion of the polymer.

Example III Two hundred and fifty parts of distilled water, 0.125 part of ammonium persulfate, 0.06 part of sodium bisulfite, and 6 parts of l-chloro-fi-hydroperfiuorohexane [H(CF2)6C1], are heated to 65 C. in a pressure vessel similar to that of Example I and the vessel is evacuated. The vessel is pressured to 58 lb ./sq. in. with tetrafiuoroethylene and shaken for 3.0 hours until the colloidal polymer first begins to coagulate. Agitation is stopped and the l-chloro-6-hydroperiiuorohexane is allowed to settle out. There is obtained a 5.93% solids dispersion of colloidal polytetrafiuoroethylene.

Example IV A mixture of two hundred parts of distilled water, 0.1 part of ammonium persulfate, 0.05 part of sodium bisulfite, 0.002 part of FeSOMI-IzO, and 10 parts of 1,2-dichlorotetrafluoroethane contained in an evacuated pressure vessel similar to that of Example I is pressured to 60 lb./sq. in. With tetrafluoroethylene and shaken at room temperature. Coagulation of the colloidal polymer product does not begin until after about 6.4 hours during which time there is produced a 1&7 solids dispersion of polytetrafiuoroethylene in which the polymer particles are surprisingly uniform in size and shape and have a mean diameter of 0.3-0.5 micron.

A control experiment without the haloethane yields a 0.75% solids dispersion of polymer in which the particles vary widely in size and shape.

Example V The process of Example III is repeated using a perfiuorinated lubricating oil having the emprical composition 0211M; in place of the l-chloro-S-hydroperfiuorohexane. In 2.1 hours there is obtained a dispersion containing 3.85% by Weight of suspended colloidal polytetrafiuoroethylene which is a concentration more than five times higher than is possible when the perfluorinated oil is omitted from the mixture.

4 Example VI Example III is repeated except that 0.001 part of FeSOUI-lzO is included and the 1-chloro-6- hydroperfluorohexane is replaced by perfiuorinated kerosene consisting only of carbon and fluorine and containing 10-14 carbons. In 1.6 hr. the concentration of colloidal polytetrafiuoroethylene is 2.74% by weight.

Although tetrafluoroethylene is perferred in the invention, chlorotrifiuoroethylene and dichlorodifiuoroethylene can be used.

Fluorine-containing compounds other than those mentioned in the Examples include 1- chloro 5 hydroperfiuoropentane, I-I(CF2) 5C1, hexafiuoroethane, CzFs, octafluoropropane, CsFs, decafiuorobutane, C4Fl0, and octafiuorocyclobutane C4F8. These saturated fluorine-containing compounds are added to the reaction mixture in proportions of from 1% to 10% by wei ht based on the total weight of reaction medium. In the polymerization of tetrafluoroethylene, the best results are obtained by adding from 1% to 5% by weight, based on the total weight of the reaction medium, of the saturated fluorine-containing compound.

The fluorine-containing compounds used in the practice of the invention claimed herein are, by comparison with the efiects I have observed With sillcones or other highly inert liquids, advantageous from the standpoint of economy and of simplicity of operation, for example, the polyfiuoroethylene monomer can be introduced into the aqueous polymerization medium as a solution in the fluorine-containing compound, and from the standpoint of obtaining aqueous dispersions containing a relatively high concentration of the completely halogenated polyflucroethylene polymers. By the present process concentrations of the latter up to 14% or more can be obtained readily.

The dispersions of this invention are useful for fabricating the polymers into a variety of forms. Films can be cast by baking fio'wouts, and in a similar manner coatings of the polymers can be applied to metal, fabrics, wood, ceramics and carbon. Coatings on metal in the form of Wire, foils, materials-handling equipment such as chemical reactors and pipe lines, structural forms, and porous articles made by casting or powder metallurgy techniques are of particular value for their inertness to moisture, corrosive chemicals, solvents and electrical and mechanical stresses. Impregnations are possible because of the small particle size of the polymers. Fabrics are advantageously impregnated to confer water repellency by procedure disclosed in my copending application S. N. 726,717, filed February 5, 1947, now U. 8. Patent 2,532,691, and glass fabrics impregnated and coated with the dispersions have unique stability and other desirable properties such as flexibility, high dielectric strength and impermeability. Coated glass fabrics prepared in this way can be used as fuel pump diaphragms and in the fashioning of resistor cores. Casting molds formed from the coated glass fabric by heat and pressure can be used as molds for lowmelting metals. Coatings on carbon and ceramics confer moisture protection with resultant increase in surface resistivity and resistance to tracking by an electric arc. The dispersions are also useful as adhesives, particularly for polytetrafluoroethylene sheeting, mica, metals and ceramics. In particular, a polytetrafiuoroethylone surface can be permanently joined to a solid substance by application of a dispersion of this invention containing at least of the polymer, drying the joint by heating at not more than 100 C. and subsequently heating the structure to above 327 C.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

The invention claimed is:

1. A process for obtaining colloidal dispersions of polymeric completely halogenated polyfluoroethylenes, said process comprising polymerizing at a temperature of 0 C. to 100 C. under a pressure of 1 to 1,000 atmospheres with agitation a monomeric completely halogenated polyfluoroethylene in an aqueous medium containing a peroxy polymerization catalyst and 1% to 10%, by total weight of said aqueous medium, of a 2- to 21-carbon atom saturated fluorine-containing compound in which any atoms contained therein other than carbon and fluorine consist of those selected from the group consisting of hydrogen and chlorine, said last mentioned atoms when contained in said fluorine-containing compound being present therein in amount of not more than one hydrogen atom and not more than two chlo rine atoms, said hydrogen and chlorine atoms being attached to chain carbon atoms substituted only with fluorine, said saturated fluorine-containing compound being liquid under the prevailing polymerization conditions.

2. The process set forth in claim 1 in which said fluorine-containing compound consists of carbon, fluorine and chlorine and contains not more than two chlorine atoms.

3. The process set forth in claim 1 in which said fluorine-containing compound consists of carbon and fluorine.

4. A process for obtaining colloidal dispersions of polymeric tetrafluoroethylene, said process comprising polymerizing monomeric tetrafluoroethylene at a temperature of 0 C. to 100 C. un- 4 der a pressure of 1 to 1,000 atmospheres with agitation in an aqueous medium containing a peroxy polymerization catalyst and 1% to 10%,

by total weight of said aqueous medium, of a 2- to 21-carbon atom saturated fluorine-containing compound in which any atoms contained therein other than carbon and fluorine consist of those selected from the group consisting of hydrogen and chlorine, said last mentioned atoms when contained in said fluorine-containing compound being present therein in amount of not more than one hydrogen atom and not more than two chlorine atoms, said hydrogen and chlorine atoms being attached to chain carbon atoms substituted only with fluorine, said saturated fluorine-com taining compound being liquid under the prevailing polymerization conditions.

5, The process set forth in claim 4 in which said fluorine-containing compound is present in the proportion of 1% to 5%, by total weight of said aqueous medium.

6. The process set forth in claim 4 in which said fluorine-containing compound consists of carbon,

- fluorine and chlorine and contains not more than two chlorine atoms.

7. The process as set forth in claim 4 in which said fluorine-containing compound is perfiuorodimethylcyclohexane.

8. The process set forth in claim 4 in which said fluorine-containing compound is 1,2-dichlorohexafluorocyclobutane.

9. The process set forth in claim 4 in which said fluorine-containing compound is l-chloro- 6-hydroperfluorohexane.

10. The process set forth in claim 4 in which said fluorine-containing compound is 1,2-dichlorotetrafluoroethane.

11. The process set forth in claim 4 in which said fluorine-containing compound is perfluorinated kerosene consisting only of carbon and fluorine and containing 10 to 14 carbon atoms.

KENNETH L. BERRY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,456,027 'Simons Dec. 14, 1948 2,559,752 Berry July 10, 1951 2,567,569 McBee Sept. 11, 1951 

1. A PROCESS FOR OBTAINING COLLOIDAL DISPERSIONS OF POLYMERIC COMPLETELY HALOGENATED POLYFLUOROETHYLENES, SAID PROCESS COMPRISING POLYMERIZING AT A TEMPERATURE OF 0* C. TO 100* C. UNDER A PRESSURE OF 1 TO 1,000 ATMOSPHERES WITH AGITATION A MONOMERIC COMPLETELY HALOGENATED POLYFLUOROETHYLENE IN AN AQUEOUS MEDIUM CONTAINING A PEROXY POLYMERIZATION CATALYST AND 1% TO 10%, BY TOTAL WEIGHT OF SAID AQUEOUS MEDIUM, OF A 2TO 21-CARBON ATOM SATURATED FLUORINE-CONTAINING COMPOUND IN WHICH ANY ATOMS CONTAINED THEREIN OTHER THAN CARBON AND FLUORINE CONSISTS OF THOSE SELECTED FROM THE GROUP CONSISTING OF HYDROGEN AND CHLORINE, SAID LAST MENTIONED ATOMS WHEN CONTAINED IN SAID FLUORINE-CONTAINING COMPOUND BEING PRESENT THEREIN IN AMOUNT OF NOT MORE THAN ONE HYDROGEN ATOM AND NOT MORE THAN TWO CHLORINE ATOMS, SAID HYDROGEN AND CHLORINE ATOMS BEING ATTACHED TO CHAIN CARBON ATOMS SUBSTITUTED ONLY WITH FLUORINE, SAID SATURATED FLUORINE-CONTAINING COMPOUND BEING LIQUID UNDER THE PREVAILING POLYMERIZATION CONDITIONS. 